dexamethasone suppression test
Jump to navigation
Jump to search
Indications
- diagnosis of Cushing's syndrome
Reference interval
- serum cortisol < 1.8-3 ug/dL (< 5 ug/dL)[2]
Principle
- Dexamethasone suppresses pituitary secretion of ACTH which, in turn, suppresses endogenous secretion of cortisol.
- cortisol assays do NOT detect dexamethasone
Predictive value of a positive test is poor (0.6%)
Predictive value of a negative test is close to 100%.
Procedure
- dexamethasone: 1 mg at 11 PM
- serum cortisol at 8 AM
Interferences
- False positives occur with:
- physiologic stress, psychologic stress
- renal failure
- estrogen therapy
- pharmaceutical agents
- endogenous depression
- incorrect timing of dexamethasone administration or of blood sampling
- significant obesity
- alcoholism
- anorexia nervosa
Management
- if 8 AM serum cortisol > 5 ug/dL
- serum ACTH*
- serum DHEA-sulfate
- urine free cortisol
- 8 mg dexamethasone suppression test* if 1 mg of dexamethasone does not fully suppress serum cortisol[2]
- serum cortisol suppresses with ACTH-secreting pituitary adenoma*
- serum cortisol does not suppress with ectopic ACTH-secreting tumor
* serum ACTH before 8 mg dexamethasone suppression test or inferior petrosal sinus ACTH
* intrapetrosal sinus sampling identifying an ACTH-secreting pituitary adenoma renders an 8 mg dexamethasone suppression test unnecessary[2]
More general terms
Additional terms
References
- ↑ Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 652
- ↑ 2.0 2.1 2.2 2.3 Medical Knowledge Self Assessment Program (MKSAP) 11, 14, 17, 18, 19. American College of Physicians, Philadelphia 1998, 2006, 2015, 2018, 2022
- ↑ Elhomsy G, Staros EB Medscape: Dexamethasone Suppression Test http://emedicine.medscape.com/article/2114191-overview